1. Field of the Invention
The present invention relates generally to a capacitive discharge igniter circuit of the kind used to ignite a difficult-to-ignite fuel by using the energy stored in a capacitor which is discharged at a threshold breakdown voltage for creating an ignition arc at the electrodes of a spark plug.
A typical environment for the use of the present invention is for systems that are used to ignite extremely dirty fuels such as fuel oils. In such systems, the fuel and contaminants can tend to short the conductive path across the electrodes of simple sparking devices and plugs; (such as generated by a 10,000 volt transformer), such that the ignition current shorts out through the dirty fuel and contaminants without generating a spark at the electrodes of the spark plug to light the fuel. This problem is normally addressed in the prior art by the use of a semiconductor material placed between the electrodes of the sparking device or by the creation of a current path of low voltage potential between the electrodes of the sparking device, whereby the space about the electrodes becomes ionized to lower resistance, thereby allowing a rapid discharge of energy stored in a capacitor between the electrodes so as to provide a hot arc for fuel ignition. It is the rapid discharge of energy, stored in a capacitor, at the electrodes of the spark plug that accounts for it""s ability to bum through contaminants and thereby generate an arc that can ignite the fuel.
2. Discussion of the Prior Art
U.S. Pat. No. 5,471,362 discloses an arc igniter circuit which has a spark plug connected in series with a spark gap device and a rectifier. A spark gap device is a relatively expensive component in which all oxygen is removed, often with getterers, and the device is then refilled with a specialty gas in such a manner that it establishes a characteristic of having a precise threshold breakdown voltage. It is this characteristic xe2x80x9cbreak down voltagexe2x80x9d that manages the circuit. The circuit is inoperable without it, and it would be beneficial to eliminate the expense of this component. A capacitor is connected in series with the spark gap and the spark plug. An electrical power source has a transformer with a primary winding supplied by an AC voltage and a secondary winding connected to the capacitor via a rectifier for charging the capacitor. The secondary winding is connected to the spark plug via a diode, thereby providing a current path for the spark gap at a predetermined voltage and simultaneously discharging the capacitor through the spark plug via the spark gap.
U.S. Pat. No. 5,793,585 discloses a similar arc igniter circuit having a high voltage power source connected to the power arc circuit downstream of a high voltage, high current diode, and by a relay connected between a power input and the power arc circuit, which has a series connection of a spark gap, a diode and a spark plug.
A capacitive discharge corona arc circuit of the type disclosed in U.S. Pat. Nos. 5,471,362 and 5,793,585 charges a capacitor which is then discharged through a corona arc circuit. This is an example of an arc being generated via a current path. These patents also mention and describe the prior art xe2x80x9cresistive pathxe2x80x9d modality mentioned above. The present invention is an evolution in that type of capacitive discharge corona arc igniter circuit, and provides a secondary power source for such power arc circuits that allows the creation of the ionized area about the electrodes of a resistive type sparking device.
FIG. 1 illustrates a prior art ignition circuit wherein a main power step-up transformer T1 (typically 2,000 V and current limiting) has an input voltage of VAC and produces an output voltage V1AC which charges a storage capacitor C1 (rapid discharge, typically 6 xcexcf at 2,000 V) through a rectifying diode D1. The capacitor C1 is then periodically rapidly discharged through a spark gap SG which is designed by a manufacturer to break down and conduct a large current, and an arc probe spark plug AP. The arc probe spark plug AP has a semiconductive resistive film across the spark plug electrodes that provides a reference ground for the discharge of the spark gap. The arc probe AP is a special type of spark plug which is designed to be in direct contact with a fuel that it is igniting, and has a semiconductive material positioned between the electrodes with a semiconductive film resistance represented as R1 in the diagram. The value of R1 can vary between a few ohms and 5 Meg ohms, and is known to change with usage.
Accordingly, it is a primary object of the present invention to provide an igniter circuit with an air gap for ignition systems of the kind used to ignite a difficult-to-ignite fuel oil by using energy stored in a capacitor which is discharged to create an ignition arc at the electrodes of a resistive arc probe spark plug.
A further object of the subject invention is the provision of a secondary power source for such power arc circuits that allows the creation of an ionized area about the electrodes of the resistive arc probe to facilitate the discharge of a stored energy source into the arc at the resistive arc probe spark plug.
The present invention advantageously uses a simple air gap, with an imprecise and irrelevant breakdown voltage, rather than a commercially available spark gap device, to eliminate the need for and expense of a commercially available spark gap device, and the costs and availability problems associated with commercially available spark gap devices. The present invention also uses a relatively simple timing circuit comprised of commercially available components to trigger its prime components.